Title page for ETD etd-07282008-134037
|Type of Document
||Hastie, Robert L.
||The effect of physical aging on the creep response of a thermoplastic composite
|Johnson, Eric R.
|Morris, Don H.
|Henneke, Edmund G. II
|Mook, Dean T.
|Stinchcomb, Wayne W.
|Date of Defense
The effect of thermoreversible physical aging on the linear
viscoelastic creep properties of a thermoplastic composite was
investigated. Radel X/IM7, an amorphous composite material
considered for use in the next generation high speed transport
aircraft, was studied. The operating environment for the
aircraft material will be near 188°C (370°F) with a service
life in excess of 60,000 hours at temperature. Accurate
predictions of the viscoelastic properties of the material are
essential to insure that design strength and stiffness
requirements are met for the entire service life.
The effect of physical aging on the creep response was
studied using momentary tensile creep tests conducted at
increasing aging times following a rapid quench from above the
glass transition temperature (Tg) to a sub-Tg aging temperature.
As the aging time increased, the creep response of the material
significantly decreased. The tensile creep compliance data
for each aging time were fit to the empirical equation for the
creep compliance D(t):
where Do, to,and m are fitting parameters determined using a
nonlinear fitting program based on the Levenberg-Marquardt
finite difference algorithm. The short-term creep compliance
curves, obtained at various aging times, were then shifted to
form a momentary master compliance curve. The doublelogarithmic
aging shift rate μ and its dependence on sub-Tg
aging temperature were determined. The aging characterization
process was conducted on unidirectional specimens with 0, 90,
and 45 degree fiber direction orientations. This permitted
the calculation of the complete principal compliance matrix
for the composite material. The effect of physical aging
becomes more apparent during long-term tests when creep and
aging occur simultaneously. This results in a gradual
stiffening and decrease in the creep response with increased
time. Predictions based solely on the Time-Temperature
Superposition Principle would significantly over-predict the
creep response if physical aging effects were ignored.
Theoretical predictions for long-term creep compliance were made using an effective time theory and compared to long-term
experimental data for each fiber orientation. Finally,
experimental results of a long-term test of a 30 degree fiber
angle orientation specimen were compared to theoretical predictions
obtained by transforming the principal compliance
matrix to the 30 degree orientation.
|| Approximate Download Time
| 28.8 Modem
|| 56K Modem
|| ISDN (64 Kb)
|| ISDN (128 Kb)
|| Higher-speed Access
next to an author's name indicates that all
files or directories associated with their ETD
are accessible from the Virginia Tech campus network only.
If you have questions or technical
problems, please Contact DLA.